Geraniums love full sun, and prefer moist, well-drained soils with a cool root zone.

The popular geranium (Pelargonium x hortorum), or zonal geranium, is prized both as an indoor plant and in the garden because of its wide variety of colorful flowers and foliage. Zonal geraniums, which are tender perennials, usually are grown as annuals and prefer moist soil. However, their preferred growing conditions make geraniums vulnerable to fungal infections. One of the most common fungi that attack geranium plants is botrytis blight, which is caused by the fungus Botrytis cinerea.

Botrytis Blight

Botrytis is spread through the air as the fine spores are lifted from the soil and carried to your geranium. Even the air caused by walking past or pruning your plant can spread botrytis spores. Botrytis fungi prefer to feed on dead or dying plant material, but if the fungus has ideal conditions for growth, it attacks living plant tissue as well. Botrytis fungi prefer cool, moist conditions. Temperatures ranging from 50 to 60 degrees Fahrenheit are ideal for its growth. Because geraniums also prefer cool, moist conditions, botrytis is a common problem for these plants.

Symptoms of Infection

Botrytis fungi prefer to feed on dead plant material, but it is hard to detect infection in the dead foliage of your geranium. However, dried leaves infected by botrytis fungus disperse a fine dust into the air when moved. These are the fungus spores. On living plant tissue, botrytis infections are indicated by fuzzy gray or brown blooms and black spots on the stems. If cool, damp conditions exist, these small black spots eat into the stem itself, consuming it entirely. On the leaves, you may see spots, lesions or large dead areas with concentric rings around them. Flowers and leaves may also begin to drop prematurely.

Cultural Control

Good sanitation practices, such as pulling weeds and keeping the soil clear of debris, are helpful in controlling botrytis blight in geraniums. Prune away infected plant parts and dispose of these in the garbage. Do not compost dead plant material infected with botrytis. Avoid watering your plants overhead. Instead, water the soil early in the day so that it has adequate time to dry before the cool evening temperatures arrive.

Chemical Control

Fungicide sprays containing chlorothalonil, copper ammonium carbonate, neem oil, potassium bicarbonate or bacillus subtilis can effectively control botrytis blight in geraniums. Apply fungicides after periods of wet weather. Fungicide sprays can contribute to moisture levels, so adequate ventilation and circulation of air around your plant are necessary to prevent further infections.

Prevention

The best way to fight botrytis infection is to prevent it from taking over your plant. Pick all dead leaves and blooms from your plant as you see them, and remove debris from the soil as well. If your geranium is growing in damp or cool conditions, thin the branches, and give plants ample space to ensure that there is enough air circulation to dry the leaves. Indoors, place your plant in an open window or near a fan to receive air that keeps the foliage and soil surface dry, and deprives the fungus of the moisture it needs to multiply.

SOURCE

​SOURCE:  http://www.pelargonium.si/jenkinsonia/griseum.htm

Edema is a disease that affects geraniums, causing leaves to yellow and die. It is thought to be due to adverse environmental conditions. Therefore, it does not spread from plant to plant. Ivy geraniums with a large root system as compared to shoot size are particularly sensitive to this disorder.

Symptoms

Small yellow spots in areas between the veins are often the first symptom observed on the top of the leaf. Small, translucent, watery pustules are seen on the underside of the leaf below the yellowed areas. These "blisters" and yellowed areas usually occur first on older leaf margins. The blisters enlarge and become brown in color and corky or scabby in texture. The entire leaf may yellow, die, and drop off. This leaf death and defoliation occurs in a pattern somewhat similar to that caused by bacterial blight.

Cause

Edema is caused by an imbalance of the water uptake and loss by the plant. A high level of water absorption by the roots is favored by warm moist soil conditions while a low level of transpiration (water loss) is favored by cool air, high relative humidity, low light levels (cloudy weather), and poor ventilation. Water retention in the cells causes some cells to burst and form watery blisters. As these broken cell areas heal, they become dry and corky.

Mite (two-spotted, Tetranychus urticae Koch) feeding may also play a role in edema development. Potter and Anderson screened ivy geranium cultivars for resistance to two-spotted spider mite attack and evaluated edema severity on the mite-infested plants. There seems to be a relationship in which mite resistant cultivars develop less severe edema than mite susceptible cultivars. The authors theorized that the plant's physiology or nutritional status that results in edema development may also favor mite survival. Edema and mite resistant cultivars were "Double Lilac White," "Sunset," "Madame Margot," "Amethyst," and "Salmon Queen". The most mite and edema susceptible cultivars included "Sybil Holmes," "Yale," and "Pascal."

Management

Edema Can Be Lessened By The Following -

Improve drainage and water less frequently;
Heat and ventilate the greenhouse to reduce humidity;
Space plants to provide good air circulation;
Water in the morning so that the soil is not too wet overnight;
Avoid wetting the leaves since wet leaves lose less water;
During cool cloudy weather, follow a watering schedule that maintains an even moisture level;
Maintain good mite control by regularly applying a miticide;

​The above information was summarized from the following sources:

Balge, R. J., Struckmeyer, B. E., and Beck, G. E. 1969. Occurrence, severity, and nature of oedema in Pelargonium hortorum Ait. Jour. Am. Soc.Hort. Sci. 94:181-183.
Digat, B. and J. Albouy. 1976. Donnees actuelles sur le probleme de l'oedeme du pelargonium. Pepinieristes Horticulteurs Maraichers 168:51-55.
Mastalerz, J. W. 1971. Geraniums. A Penn State Manual. Pennsylvania Flower Growers. 103 Tyson Bldg., University Park, PA 16802. 350 pp.
Potter, D. A. and R. G. Anderson. 1982. Resistance of ivy geraniums to the two-spotted spider mite. J. Am. Soc. Hort. Sci. 107:1089-1092.

SOURCE: extension.psu.edu/edema-of-geranium

Over a century ago, Reunion Island in the Indian Ocean used to be the world's leading producer of geranium oil - a fragrant oil used in cosmetics and culinary dishes.
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But over the past 100 years the industry has all but died out on the island as countries like South Africa and China have stepped up commercial production.

​VIDEO:  BBC NEWS

1. A genuine South African

Geranium – a name that sounds like typical Bavarian farmhouse facades, a traditional German balcony boxer. But the geranium is actually an immigrant. It was originally a native of South Africa, where more than 250 wild species of the plant still grow. The first geraniums did not come to Europe until the17th century. From the Netherlands the plant then embarked on its triumphant advance across the globe.

2. Living by the wrong name

From the botanical perspective the geranium is not a member of the Geranium family. To gardeners and botanists “geranium” refers to a winter-hardy perennial shrub. The popular summer bloomers, on the other hand, are known among the experts as “pelargoniums”. The confusion about the name can be traced back to the 17th century. At that time, the first pelargoniums which were brought to Europe from South Africa were called geraniums, due to their similarity to the domestic perennial plant. Not until the 18th century did botanists recognize the differences between them and gave the genus from South Africa the name Pelargonium. Yet in many countries the correct name has never been adopted in common parlance.

3. Cultural commodity and symbol of homeland

Astonishingly enough, not only people in Germany but also in other European countries consider the geranium an integral part of their culture and a symbol of their homeland. The Swiss have even elected this easy-care blooming beauty their national flower. One wonders if there is a connection: In the 19th century pelargoniums were flourishing all across Europe, at a time when a feeling of national pride was growing in many countries.

4. Stylish room deco

Geraniums not only adorn balconies, terraces and gardens, they also make stylish room decorations. In particular the regal geranium was originally cultivated as a houseplant, and it also goes well with modern interiors. But other geraniums, such as angel and scented-leaved geraniums, also feel at home in a sunny spot indoors, where they create a gaily-coloured summer feeling. Or a really easy solution: just a few geraniums-stems in a vase or in a bouquet.

5. Culinary qualities

Bon appetit! The leaves and flowers of scented geraniums are edible. Thanks to the essential oils in their leaves, they lend not only decorative touches but also a fine aroma to meat dishes, salads and desserts. For examples, varieties with a lemon aroma add zest to salads, sorbets or tea. Rose geraniums lend a sophisticated note to puddings, cakes, jams or desserts, while geraniums with a peppermint scent are a wonderful addition to homemade lemonade. And creative cooks will put to good use to the many other aromas of scent-leaved geraniums, which range from apple to orange and peach to chocolate and cinnamon. Let’s get cooking!

6. Healing powers

Geraniums are not only decorative, but some also have healing powers. The roots of the Cape region pelargonium, for example, were used by the indigenous people of South Africa to treat respiratory disease, and to this day are a main ingredient of the natural remedy “Umckaloabo”. The essential oils in certain types of scented geraniums help alleviate depression and stress.

7. Natural insect repellent

Certain scent-leaved geraniums can effectively ward off insects, thanks to the essential oils contained in their leaves. At the slightest breeze or the lightest touch, these plants release their perfume. What may be a pleasant smell to us humans will send mosquitoes, wasps and other pesky insects on their way. The best insect repellents are geraniums with lemon and orange aromas.

8. Immense spectrum of varieties

Most people know geraniums as those bright red or white balcony boxers. Fact is, this plant is much more than that: The geranium is astonishingly versatile with its huge diversity of colours, leaves and flower shapes, sizes and growth forms. They not only bloom in red, white and pink, but also in many modern shades such as pink, violet, lilac, apricot, orange and yellow. And they come in a wide range of bicolour variants.

9. Bountiful blooms even without a green thumb

Geraniums are perfectly suited for people who can’t or don’t want to spend a lot of time caring for their plants. Because hardly any other plant is as easy-care and durable. Even those who do not have a green thumb can achieve a beautiful display of flowers with minimum time and effort.

10. Record breaker

When given proper care, geraniums can achieve record-breaking size. In the internet one can find specimens that have supposedly achieved heights of five metres or a circumference of more than ten metres.

Source:  Press Release

​Q. What is the difference between seed geraniums and zonal ones? Are there other types?

A. Seed geraniums are a form of zonal geranium that has been grown from seed rather than from tissue cuttings.

Both have zones of color in the leaves (that's how they get the name "zonal"), but seed geraniums are usually more compact and are often the cheapest option. Varieties differ, but they usually have lots of 3- to 4-inch flower heads. Most grow about a foot tall and wide. They are a great option for a mass planting.

Plants labeled "zonal geraniums" can have flower heads up to 6 inches across and, unlike seed geraniums, often have double flowers. But, they usually don't have as many flowers as the seed varieties. The zonal plants grow more upright and can be up to 18 inches tall. As new varieties are developed, you will see fewer differences between the seed- and tissue-propagated zonal varieties.

There are two new kinds of zonals that you may see in garden centers. For something different, look for stellar and fancy-leaf varieties.

Some other types of plants commonly sold as annual geraniums are, ivy-leaf, regal and scented-leaf. Ivy-leaf geraniums have waxy leaves that, well, look like ivy. They trail and are great in hanging baskets.

Regal geraniums, such as Martha Washington, are commonly sold as houseplants. They need cool nights to flower.

Scented leaf varieties flower, but not as impressively as other types. They are grown for the leaves, which can smell like roses, lemons, apples or mints. There is one that smells like citronella and is supposed to repel mosquitoes, but there is no proof that it works.

To confuse things a little more, these plants are called geraniums but are actually pelargoniums. Pelargoniums can be overwintered indoors or grown as a houseplant. True geraniums, sometimes called hardy geraniums or cranesbills, are tough perennials that can be planted outside and, depending on the variety, are hardy down to zone three. Like pelargoniums, they are usually ignored by deer. They don't have big balls of flowers like zonal pelargoniums, but their smaller blossoms and pretty foliage are a great addition to our gardens.

Source:  U of M Extension Master Gardeners in St. Louis County

Overview and Description

We know them as simply "geraniums". They are one of the most popular container plants, yet they are not really geraniums at all. Botanically they are Pelargonium. How's that for a mouthful? There are true geraniums, the perennial cransbills, but they look little like the annul plants we commonly call geraniums.

The confusion with the names can be traced back to disagreements between botanists over classification and is of little importance to most gardeners, except for the distinction that perennial cransbill geraniums will come back each year and zonal geraniums, those now classified as Pelargonium, are topical perennials usually grown as annuals.

They got the prefix "zonal" because of the markings on their leaves.

Zonal geraniums were discovered in South Africa and if you have a similar, tropical climate, you can grow them as perennials. Along with zonal geraniums, there are 3 more commonly grown types of Pelargonium:

1. Ivy-Leaf Geranium (Pelargonium peltatum) – As their name implies, these geraniums have a trailing habit and ivy-shaped leaves. The flowers are smaller and less showy than zonal geraniums and the plants are often used as spillers in containers.
2. Scented-Leaf Geranium (Pelargonium domesticum) – Scented geraniums get their fragrance from the oil in their leaves. They can mimic all kinds of scents, like lemon, rose, mint, pine, fruits and even chocolate. The flowers tend to be small and often insignificant and the leaf shapes will vary. Besides their ornamental and fragrant appeal, many can also be used in cooking.
3. Regal and Angel Geraniums (Pelargonium domesticum) – The Regals, also referred to as Martha Washington geraniums, are full, bushy plants with flowers in unusual colors and

Zonal geraniums are bushy plants, mainly used for containers and bedding. There has been considerable breeding done, particularly for size and abundance and colors of flowers, so there is a good deal of variety.

• Leaves: Oval leaves grow on succulent stems. The leaves often have zones of maroon or bronzy-green.

• Flowers: Flowers can be single (5 petals) or double and come in clear white, pink, salmon, orange, red, magenta, lavender and bi-colors.

Botanical Name:Pelargonium x hortorum

Common Name:Geranium, Zonal Geranium

Hardiness Zones: USDA Hardiness Zones 9 -12. Zonal geraniums are basically tropical perennials. Although they are often grown as annuals, they may over-winter in zones as cool as Zone 7, if they have some protection and the winter is mild.

Sun Exposure: Full sun to Partial Shade. They will bloom best in full sun.

Mature Size: Size will vary with variety. There are some dwarf geraniums that will never get more than 5 - 6 inches tall and newer varieties being bred for height and spread. In general, most are between 5 - 24 inches (12 - 60 cm) H x 12 - 15 inches (30 - 38 cm) W.

Bloom Period: Zonal geraniums start blooming in mid-spring and will repeat bloom until frost. Deadheading the entire flower stalk after the flower fades will encourage more blooms.

Suggested Varieties:

• 'Appleblossom Rosebud' - Pom-pom flowers in a pink and white bi-color.
• 'Black Velvet Rose' - Dark, chocolate-brown leaves with only a narrow band of green and bright rose-pink flowers.
• 'Calliope Dark Red' - a cross between zonal and ivy-leaved, with double, dark-red flowers.

• 'Divas Orange Ice' - an F1 hybrid with bi-colored white and soft orange flowers that look like creamsicles.

Every year there are more and more choices. If you find a good source, there are Pelargoniums that are tulip-flowered, cactus-flowered and spiky star-shaped flowers. There are also the fancy-leaved varieties, grown more for their variegated and patterned foliage.

Design Suggestions: Zonal geraniums have gotten a bad reputation by plant snobs. They've been considered garish and common. Too many of the brightly colored plants can start to look over the top, but these plants are excellent in all kinds of containers. The brighter reds are very elegant all alone and pair well with flowers in equally bright colors, like portulaca or nasturtium.
The softer pinks and salmons complement blue and purple flowers and the lavender shades really stand out next to the chartreuse foliage of Huechera or sweet potato vines.

Growing Tips

Soil: Zonal geraniums are not terribly fussy about soil pH, but prefer a slightly acid soil of about 5.8 to 6.5.  (It's essential that the soil be well draining - these plants don't like to be wet for long!)

Planting: You can start zonal geraniums from seed, cuttings or transplants. Taking cuttings was the traditional method of propagating geraniums and maintaining favorite varieties. If you choose to take cuttings, make sure you only use healthy, vigorous plants.

Starting Geraniums from Seed: Geranium can easily be started from seed, although the seed is usually for F1 hybrids. Seed geraniums are bred to be disease resistant and to bloom well in the heat of summer.

Start seeds 8 - 10 weeks before your last frost date. They can take up to 2 weeks to germinate and should be kept warm, 70̊ and 75̊F (21̊ - 24̊C), and moist in the process. Scarifying the seed before planting will help aid germination.

Harden off young plants before planting outdoors. They should begin to bloom about a month after being set out.

Maintenance:
Zonal geraniums are not heavy feeders, but since they are usually grown in containers, a light feeding with your favorite fertilizer, every 2-4 weeks, will keep them vigorous.

Stressing them slightly by watering only after the soil has dried out completely for a day or two seems to encouraging more profuse blooming. Just don't leave them dry for so long they start dropping leaves and declining.

If you don't live in USDA Zone 9 or higher, your plants will need some winter protection. You can bring them in and grow them as houseplants, in a bright, direct light window. You could take cuttings in mid-summer and bring these smaller plants indoors, or you can over winter your geraniums in their dormant state.

Pests & Problems:For the most part, zonal geraniums are not prone to insect pests, when grown outdoors. Indoors, aphids and whiteflies can become a nuisance.

There are a few fungal and bacterial diseases to look out for, mainly

• Stem or root rot caused by poorly drained soil.
• Gray mold or botrytis, especially in humid or damp weather, which causes grayish fuzz on the leaves and eventually a slimy mush.

Special thanks to the National Garden Bureau which named Pelargonium its 2012 Plant of the Year and provided research for this article.

BY:  MARIE IANNOTTI
Updated 01/20/17

Black Leg of Geranium
M. Grabowski, UMN Extension Educator

Black leg is a stem infection of Geraniums (Pelargonium spp.) that results in a distinctive black discoloration of stems. As infected stems rot, they become soft and often bend over. This disease is caused by several species of the water mold Pythium. Pythium spp. are soil dwelling organisms that thrive in wet conditions and can survive in infected plant debris and soil. Black leg symptoms often start at the soil line and move up the plant.

To avoid black leg, inspect all geraniums prior to purchase and select only healthy symptom free plants. If repotting geraniums, use new clean potting mix and new pots or pots that have been cleaned with a solution of 10% household bleach. Take care to keep tools, watering cans, and hose heads off the floor and away from dirt and plant debris. Pythium spp. can be introduced into clean potted plants by tools that have contacted contaminated dirt or plant debris. Do not over water plants.

If plants do become infected, they will not recover. Discard the plant and the potting mix. Clean the pot with a solution of 10% household bleach before reusing it.

​Source:  Black Leg

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​Is it a Geranium? Is it an Erodium? No it's a Pelargonium!

One of the most confusing generic names to any gardener is Geranium. Anyone familiar with temporary planting schemes will know the popular Bedding Geraniums. This is the rather misleading common name for hybrids of the genus Pelargonium (mainly derived from Pelargonium zonale). To distinguish them, true Geranium are often called Hardy Geraniums. Most species and hybrids of true Geraniums are able to tolerate several degrees of frost, and therefore can live outside all year round, even in cold climates. So you cannot talk just about a geranium, you have to clarify whether you mean a Bedding Geranium or a Hardy Geranium, ie. Pelargonium or Geranium respectively.

Fortunately, the two genera are quite easy to tell apart. Geraniums have flowers with 5 more or less identical petals, usually arranged in a flat or bowl shaped. Pelargoniums also have 5 petals but they are arranged 2 above and 3 below. The 2 upper petals are usually larger and broader than the lower 3 (indeed in some species the lower 3 are even missing). So Geranium flowers have radially symmetric flowers (actinomorphic), whereas Pelargonium flowers have a single plane of symmetry (zygomorphic).

This brings us on to Pelargonium incarnatum, which grows here at Phillipskop Mountain Reserve (Phillipskop Mountain Reserve is 246ha (608 acres) in size and occupies the southerly slopes of the Klein River Mountains just to the east of Stanford, on the Western Cape of South Africa).  In almost every genus there is one species that refuses to obey the rules. This species of Pelargonium has perfectly radially symmetric flower. So how do we know this is a Pelargonium and not a Geranium (for there are a number of true Geranium species that grow in South Africa)? One way is to count the stamens. A true Geranium will have 10 fertile stamens (have anthers with pollen) whereas Pelargoniums will always have 7 or fewer. The remaining stamens in Pelargonium are modified in some way but always lack an anther. In Pelargonium incarnatum one can clearly see just 5 fertile stamens.

Source:  Pelargonium Incarnatum